有或没有句柄的嵌套classdef? [英] Nested classdef with or without handle?

问题描述

我正在尝试使用Matlab中的可更新对象(类)和嵌套类.我观察到似乎是由于手柄状态引起的行为.

I am trying to used updatable object (class) in Matlab with nested class. I observe a behavior that seems to be due to the handle status.

我写了两个类testA和testB. testB是将类testA作为属性调用的主要类:

I write the 2 classes testA and testB. testB is a the main class that calls the class testA as a property:

classdef testB 
    properties
        objA=testA;
    end
    methods
        function obj=testB()
            obj.objA
            if isempty(obj.objA.val)
                obj.objA.val=5;
            else
                 obj.objA.val=obj.objA.val+5;
            end
        end
        function up(obj)
            obj.objA.val=obj.objA.val+6;
            obj.objA.val
        end
    end
end

首先，testA是一个句柄类.

classdef testA < handle 
    properties
        val=[];
    end
    methods
        function obj=testA()
        end
        function set.val(obj,tt)
            obj.val=tt;
        end
    end
end

当我两次创建testB对象时

tt=testB
tt=testB

我发现testA中的val属性没有重新初始化(testA中的val保留了以前的值).我不确定，但这似乎是由于handle功能所致.方法tt.up按预期增加testA中的val属性.

I observe that the val property in testA is not reinitialized (val in testA keeps the previous value). I am not sure but it seems to be due to the handle feature. The method tt.up increase the val property in testA as expected.

第二，如果我将testA类更改为值类.

Secondly if I change the testA class to a value class.

classdef testA  
    properties
        val=[];
    end
    methods
        function obj=testA()
        end
        function obj=set.val(obj,tt)
            obj.val=tt;
        end
    end
end

在这种情况下，每次testB的新实例和testA的新实例时，都会连续创建tt=testB的调用.不幸的是，在这种情况下，up方法无法按预期方式工作(val的新计算值未存储在对象中).

In this case the successive calls of tt=testB create each time a new instance of testB with a new instance of testA. Unfortunately in this case the up methods does not work as expected (the new computed value of val is not stored in the object).

一种解决方案是在完全初始化testB对象之前，考虑为testA使用handle类，并强制将其删除.但是我不知道该怎么做.

A solution could be to consider handle class for testA and force to delete it before fully initialize the testB object. However I don't know how to do this.

推荐答案

这是已记录的行为:在您的testB定义中，obj=testA仅在加载类定义时被评估一次.该类的所有实例都将引用相同的句柄类对象.

This is documented behavior: in your testB definition, obj=testA is evaluated only once, when the class definition is loaded. All instances of the class will have a reference to the same handle class object.

只需在同一文档页面上，您将会看到，如果您要为每个testB实例使用不同的testA实例，则应该在testB的构造函数中创建testA的新实例:

Just below on same documentation page you'll see that you should create a new instance of testA in the constructor for testB, if you want a different instance of testA for each instance of testB:

classdef testB 
    properties
        objA
    end
    methods
        function obj=testB()
            objA = testA;
            % ... further initialization
        end
    end
end

这篇关于有或没有句柄的嵌套classdef?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！